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Date: Tue, 24 Apr 2018 16:34:52 +0800
From: Yanjun Zhu <yanjun.zhu@...cle.com>
To: Doug Ledford <dledford@...hat.com>, monis@...lanox.com,
jgg@...pe.ca, linux-rdma@...r.kernel.org
Cc: netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/1] IB/rxe: avoid double kfree_skb
Hi, all
rxe_send
ip_local_out
__ip_local_out
nf_hook_slow
In the above call process, nf_hook_slow drops and frees skb, then -EPERM
is returned when iptables rules(iptables -I OUTPUT -p udp --dport 4791
-j DROP) is set.
If skb->users is not changed in softroce, kfree_skb should not be called
in this module.
I will make further investigations about other error handler after
ip_local_out.
If I am wrong, please correct me.
Any reply is appreciated.
Zhu Yanjun
On 2018/4/20 13:46, Yanjun Zhu wrote:
>
>
> On 2018/4/20 10:19, Doug Ledford wrote:
>> On Thu, 2018-04-19 at 10:01 -0400, Zhu Yanjun wrote:
>>> When skb is dropped by iptables rules, the skb is freed at the same
>>> time
>>> -EPERM is returned. So in softroce, it is not necessary to free skb
>>> again.
>>> Or else, crash will occur.
>>>
>>> The steps to reproduce:
>>>
>>> server client
>>> --------- ---------
>>> |1.1.1.1|<----rxe-channel--->|1.1.1.2|
>>> --------- ---------
>>>
>>> On server: rping -s -a 1.1.1.1 -v -C 10000 -S 512
>>> On client: rping -c -a 1.1.1.1 -v -C 10000 -S 512
>>>
>>> The kernel configs CONFIG_DEBUG_KMEMLEAK and
>>> CONFIG_DEBUG_OBJECTS are enabled on both server and client.
>>>
>>> When rping runs, run the following command in server:
>>>
>>> iptables -I OUTPUT -p udp --dport 4791 -j DROP
>>>
>>> Without this patch, crash will occur.
>>>
>>> CC: Srinivas Eeda <srinivas.eeda@...cle.com>
>>> CC: Junxiao Bi <junxiao.bi@...cle.com>
>>> Signed-off-by: Zhu Yanjun <yanjun.zhu@...cle.com>
>>> Reviewed-by: Yuval Shaia <yuval.shaia@...cle.com>
>> I have no reason to doubt your analysis, but if there are a bunch of
>> error paths for net_xmit and they all return with your skb still being
>> valid and holding a reference, and then one oddball that returns with
>> your skb already gone, that just sounds like a mistake waiting to happen
>> (not to mention a bajillion special cases sprinkled everywhere to deal
>> with this apparent inconsistency).
>>
>> Can we get a netdev@ confirmation on this being the right solution?
> Yes. I agree with you.
> After iptables rule "iptables -I OUTPUT -p udp --dport 4791 -j DROP",
> the skb is freed in this function
>
> /* Returns 1 if okfn() needs to be executed by the caller,
> * -EPERM for NF_DROP, 0 otherwise. Caller must hold rcu_read_lock. */
> int nf_hook_slow(struct sk_buff *skb, struct nf_hook_state *state,
> const struct nf_hook_entries *e, unsigned int s)
> {
> unsigned int verdict;
> int ret;
>
> for (; s < e->num_hook_entries; s++) {
> verdict = nf_hook_entry_hookfn(&e->hooks[s], skb, state);
> switch (verdict & NF_VERDICT_MASK) {
> case NF_ACCEPT:
> break;
> case NF_DROP:
> kfree_skb(skb); <----here, skb is freed
> ret = NF_DROP_GETERR(verdict);
> if (ret == 0)
> ret = -EPERM;
> return ret;
> case NF_QUEUE:
> ret = nf_queue(skb, state, e, s, verdict);
> if (ret == 1)
> continue;
> return ret;
> default:
> /* Implicit handling for NF_STOLEN, as well as
> any other
> * non conventional verdicts.
> */
> return 0;
> }
> }
>
> return 1;
> }
> EXPORT_SYMBOL(nf_hook_slow);
>
> If I am wrong, please correct me.
>
> And my test environment is still there, any solution can be verified
> in it.
>
> Zhu Yanjun
>>
>>> ---
>>> drivers/infiniband/sw/rxe/rxe_net.c | 3 +++
>>> drivers/infiniband/sw/rxe/rxe_req.c | 5 +++--
>>> drivers/infiniband/sw/rxe/rxe_resp.c | 9 ++++++---
>>> 3 files changed, 12 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/infiniband/sw/rxe/rxe_net.c
>>> b/drivers/infiniband/sw/rxe/rxe_net.c
>>> index 9da6e37..2094434 100644
>>> --- a/drivers/infiniband/sw/rxe/rxe_net.c
>>> +++ b/drivers/infiniband/sw/rxe/rxe_net.c
>>> @@ -511,6 +511,9 @@ int rxe_send(struct rxe_pkt_info *pkt, struct
>>> sk_buff *skb)
>>> if (unlikely(net_xmit_eval(err))) {
>>> pr_debug("error sending packet: %d\n", err);
>>> + /* -EPERM means the skb is dropped and freed. */
>>> + if (err == -EPERM)
>>> + return -EPERM;
>>> return -EAGAIN;
>>> }
>>> diff --git a/drivers/infiniband/sw/rxe/rxe_req.c
>>> b/drivers/infiniband/sw/rxe/rxe_req.c
>>> index 7bdaf71..9d2efec 100644
>>> --- a/drivers/infiniband/sw/rxe/rxe_req.c
>>> +++ b/drivers/infiniband/sw/rxe/rxe_req.c
>>> @@ -727,8 +727,9 @@ int rxe_requester(void *arg)
>>> rollback_state(wqe, qp, &rollback_wqe,
>>> rollback_psn);
>>> - if (ret == -EAGAIN) {
>>> - kfree_skb(skb);
>>> + if ((ret == -EAGAIN) || (ret == -EPERM)) {
>>> + if (ret == -EAGAIN)
>>> + kfree_skb(skb);
>>> rxe_run_task(&qp->req.task, 1);
>>> goto exit;
>>> }
>>> diff --git a/drivers/infiniband/sw/rxe/rxe_resp.c
>>> b/drivers/infiniband/sw/rxe/rxe_resp.c
>>> index a65c996..6bdf9b2 100644
>>> --- a/drivers/infiniband/sw/rxe/rxe_resp.c
>>> +++ b/drivers/infiniband/sw/rxe/rxe_resp.c
>>> @@ -742,7 +742,8 @@ static enum resp_states read_reply(struct rxe_qp
>>> *qp,
>>> err = rxe_xmit_packet(rxe, qp, &ack_pkt, skb);
>>> if (err) {
>>> pr_err("Failed sending RDMA reply.\n");
>>> - kfree_skb(skb);
>>> + if (err != -EPERM)
>>> + kfree_skb(skb);
>>> return RESPST_ERR_RNR;
>>> }
>>> @@ -956,7 +957,8 @@ static int send_ack(struct rxe_qp *qp, struct
>>> rxe_pkt_info *pkt,
>>> err = rxe_xmit_packet(rxe, qp, &ack_pkt, skb);
>>> if (err) {
>>> pr_err_ratelimited("Failed sending ack\n");
>>> - kfree_skb(skb);
>>> + if (err != -EPERM)
>>> + kfree_skb(skb);
>>> }
>>> err1:
>>> @@ -1141,7 +1143,8 @@ static enum resp_states
>>> duplicate_request(struct rxe_qp *qp,
>>> if (rc) {
>>> pr_err("Failed resending result.
>>> This flow is not handled - skb ignored\n");
>>> rxe_drop_ref(qp);
>>> - kfree_skb(skb_copy);
>>> + if (rc != -EPERM)
>>> + kfree_skb(skb_copy);
>>> rc = RESPST_CLEANUP;
>>> goto out;
>>> }
>>> --
>>> 2.7.4
>>>
>
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